An inflatable vehicle occupant protection device, such as an air bag, is deployed upon the occurrence of a vehicle crash. The air bag is part of a vehicle occupant protection apparatus which further includes a crash sensor and an inflator. The crash sensor senses vehicle conditions that indicate the occurrence of a crash. When the crash sensor senses a crash-indicating condition of at least a predetermined threshold level, the inflator is actuated. The inflator then emits inflation fluid which inflates the air bag into the vehicle occupant compartment. When the air bag is deployed in this manner, it helps to protect an occupant of the vehicle from a forceful impact with parts of the vehicle as a result of the crash.
A particular type of air bag inflator contains inflation fluid under pressure. Such an inflator is disclosed in U.S. Pat. No. 5,348,344. In the inflator disclosed in the '344 patent, the inflation fluid is an ingredient in a mixture of gases. The mixture of gases further includes a fuel gas which, when ignited, heats the inflation fluid.
The inflator has an igniter containing a small charge of pyrotechnic material. When the air bag is to be inflated, the igniter is actuated electrically. The pyrotechnic material is then ignited and produces combustion products which, in turn, ignite the fuel gas. The fluid pressure inside the inflator is increased by the heat generated upon combustion of the fuel gas. The inflation fluid then flows outward from the inflator and into the air bag to inflate the air bag more quickly than if the inflation fluid had not been heated and further pressurized.
The manner in which the inflating air bag affects movement of the vehicle occupant can be influenced by factors such as the force with which the occupant moves against the air bag and the pressure of the inflation fluid in the air bag. Those factors, in turn, can be influenced by vehicle conditions such as the severity of the crash, and/or by vehicle occupant conditions such as the size, weight and position of the occupant.